This week's programme in the series on Man and Science today.

We are all quick to notice how we differ from each other, tall or short, fair or dark. But we seldom realise how much we are all alike. We expect to have five fingers on each hand, two ears and a nose in the middle.

But how does it happen? As we grow from a minute egg, a single cell, chemicals have to be made, cells have to be organised, and tissues laid down in exactly the right place at exactly the right time - and it happens again and again with such accuracy that we take it completely for granted - even with our children.
But obviously something must determine why eyes become eyes and fingers become fingers. It can't be chance.

It also happens in nature - what are the rules which govern the spreading of a chestnut tree? Why do the patterns on the feathers of a duck come back at each generation? The mystery once seemed insoluble, but now, suddenly, a small group of biologists are finding startlingly simple clues to the way living forms develop.

Supposing we can ultimately reveal the secret of growth and form, of normality. What next? We could have the power to tamper with the very nature of ourselves.